Narrowing of the coronary arteries due to atherosclerosis is commonly treated by implantation of a stent, using a catheter, to hold the artery open. In a large fraction of cases, however, the treated artery closes up again due to in-stent restenosis, necessitating further treatment. Accurate assessment of such restenosis generally requires re-catheterization. A number of non-invasive techniques have been proposed, such as in U.S. Pat. No. 6,729,336, in which an electromagnetic wave transmitter is used to excite a stent, and an acoustic sensor detects stent acoustic oscillations.
RF imaging is best known in the context of radar systems, but RF diagnostic imaging systems have also been developed for medical applications. For example, U.S. Patent Application Publication 2008/0169961, whose disclosure is incorporated herein by reference, describes computerized tomography using radar, which may be used for generating an image of living tissue. As another example, U.S. Pat. No. 7,454,242, whose disclosure is incorporated herein by reference, describes tissue-sensing adaptive radar imaging for breast tumor detection.
Various antenna designs have been proposed for RF imaging of body tissues. For example, U.S. Pat. No. 6,061,589, whose disclosure is incorporated herein by reference, describes a microwave antenna for use in a system for detecting an incipient tumor in living tissue, such as that of a human breast, in accordance with differences in relative dielectric characteristics. A composite Maltese Cross or bow-tie antenna construction is employed to irradiate the living tissue and to collect backscatter or other scatter returns.